Lifeboat Foundation Space Habitats

Overview

Establishing self-sufficient space habitats will serve as a backup plan
for human civilization. A number of key milestones need to be reached
before the long-term development of space is feasible, however. Improved
access to space will catalyze the establishment of such habitats by
allowing more frequent and less expensive flights beyond the atmosphere.
Innovative, non-rocket methods of reaching orbit will enable more
substantial progress in space. Artificial ecosystems will need to be
made as independent as possible to minimize the need for new resources.
Better management of and access to resources from non-terrestrial bodies
will allow astronauts to get the most out of what they do have. Finally,
further countermeasures against the effects of space on health will be
required to sustain human life in space.

The Lifeboat Foundation has begun design on Ark I, a self-sustaining
space habitat. We support the efforts by SpaceX and others to make
access to space more affordable. Likewise, we support the efforts of
Bigelow Aerospace and others to develop habitable environments in space.

Improved Access to Space

After more than fifty years of development, launch vehicles (rockets
that reach space) still have severe limitations in what they can get
into space. It appears extraordinarily difficult to increase the
dimensions of a rocket’s payload volume, which restricts payloads to a
certain size. For this reason, space structures have been built by
assembling separate, smaller modules. Inflatable modules may increase
this upper limit on module size, but fundamental limitations will always
exist with launch vehicle technology. Furthermore, the high cost of
rocket launches prohibits all but large corporations, governmental
agencies, and the wealthiest of tourists from reaching low Earth orbit.
Improvements in the economics of launch vehicles can reduce the cost of
accessing space in the short term, but radical non-rocket space launch
technologies will be required in the long term.

Many such ideas have been proposed, but it’s difficult to meaningfully
compare them and get a sense of what’s actually on the technology
horizon. The best way to quantitatively assess these technologies is by
using Technology Readiness Levels (TRLs). TRLs are used by NASA, the
United States military, and many other agencies and companies worldwide.
Typically there are nine levels, ranging from speculations on basic
principles to full flight-tested status.

Below is a survey of existing ideas for reaching space without relying
on rockets.

Space Gun TRL 6

Space guns are not intended to transport humans, but they may one day
hurl cargo or robotic equipment into space. In a gun, all of the
positive acceleration of a projectile takes place inside the barrel.
The same is true of a space gun. Like with a bullet, this requires that
a projectile undergo a tremendous amount of acceleration. It must
accordingly be very rugged; a weak projectile would not survive intact.
Nonetheless, the US Navy’s HARP Project launched a projectile to 180
kilometers-around the boundary of low Earth orbit. A robust projectile
could be brought into a stable orbit by attaching a small rocket to it.

Space Plane TRL 6

A version of a space plane called SpaceShipOne reached a 100 kilometer
altitude on June 21, 2004. It was also the first privately-funded
venture into space. While showing great promise for reaching suborbital
trajectories, fully orbital space planes will likely suffer all the
drawbacks of the Space Shuttle. Winged lifting bodies need to carry
their own propellant and oxidizer when in space, and this requirement
tends to lead to an aerodynamic shape that does not fly well in the
atmosphere. Despite the apparent limitations of space planes, they will
probably benefit substantially from breakthroughs in propulsion and
materials science. The Boeing X-37 is a small unmanned space plane
being operated by the US Air Force. A proposal for combining a form of
space plane with a tether system for orbital transfer is mentioned in
the section below on tether systems. It will be interesting to see
whether space planes are ever developed for human transport into orbit.

Mass Driver TRL 4

A mass driver, also called an electromagnetic catapult, uses
non-propulsive methods to get a vehicle up to speed. It would likely
resemble a magnetically-levitating train whose track curved upward into
the sky. Even if only half a vehicle’s final velocity could be
delivered by the mass driver, it would cut the required rocket fuel down
by much more than half. Most of a traditional rocket’s fuel is used at
the beginning of flight to push other stored fuel; as soon as it is
lighter, a small amount of fuel can deliver a much larger acceleration.
A vehicle that carried humans and cargo into space from a mass driver
would probably require some amount of rocket power for the later part of
the trip.
An additional advantage of a mass driver is that the heaviest air
resistance would be at the bottom of the track. A vehicle would not
need to use fuel to fight this air resistance. The summit of Mt.
Everest has an air pressure of only one third that of sea level. It
might be optimal, therefore, to build such a structure up the side of a
tall mountain. If a vehicle was sent up the west side of a mountain, it
could also take advantage of the Earth’s eastward rotation to get a
boost in velocity. A mass driver would certainly be a colossal project,
but it would require no major technological breakthroughs.

Space Elevator TRL 3

The space elevator concept has been around for decades. Rather than
building the structure upwards, it actually hangs from geostationary
orbit. An object in geostationary orbit always remains above the same
point on Earth’s equator-if a space elevator had its center of mass
positioned here, it would need no structural support from Earth. A
cable would then hang down to the surface. Another cable would “hang”
out into space as a counterweight to keep the center of mass in
geostationary orbit. Some kind of vehicle, often called a climber,
would then carry payloads up the cable to the desired height or
velocity. The space elevator has also been called a “skyhook” because
of how it hangs down from space.

Major technological challenges for the space elevator persist,
specifically finding a material strong and light enough to use as a
cable. The cable would need to be more than 22,000 miles (35,000
kilometers) long, which is considerably longer than the diameter of
Earth itself. Supporting its own weight would be the primary
difficulty. Advances in nanotechnology, particularly in carbon
nanotubes, may prove promising for space elevators. Other challenges
include terrestrial weather hazards, impacts with meteoroids and
orbiting objects, and repair options.

Tether Systems TRL 2

Tether propulsion involves transferring momentum between two spacecraft.
As a method of non-rocket space launch, a tether system could help boost
a space plane from a suborbital trajectory to a full orbital flight
path. For this to work, a spinning tether station must be in an orbit
that allows it to dip to a very low altitude-near the lower boundary of
space. Such an altitude, however, would require it to move very fast
compared to aircraft speeds. To allow for a rendezvous between space
plane and station, a very fast plane must be used. The tether station
also must extend one or more tethers outward and spin to reduce the
velocity of the tether tips at low altitude. Though the station would
be orbiting, it would appear as if it were “rolling” on the top of the
atmosphere, with the bottom position of the tethers moving much slower
than the top. The slower-moving ends of tethers at low altitudes would
allow fast-moving space planes to latch on.

Tether systems, which require tethers kilometers in length, generally
must face the same risks of impact with orbiting objects as the space
elevator does. There is the additional challenge of getting the space
plane in position at the right time, latching on, and unlatching at the
right time. Though no tether propulsion system has yet been tested,
these concepts are gaining more attention in recent times. Prospects
for tether systems will benefit from advances in materials science and
aeronautics research.

Flow of Resources

A variety of technologies are being pursued to help reuse and recycle
resources in space. Astronauts aboard the International Space Station
(ISS) already reuse water, which in the end is much more pure than
public water in a typical developed city. Plants can allow for the
exchange of carbon dioxide for oxygen, and can eventually provide food
matter by using waste as fertilizer. Packaging of goods will be made to
be as recyclable as possible out of practical necessity. This process
of creating an artificial ecosystem is commonly referred to as “closing
the loop”, and will minimize the need for new resources.

The process of obtaining resources from an extraterrestrial
environment-such as the Moon, Mars, or an asteroid-is called in-situ
resources utilization (ISRU). ISRU techniques may allow astronauts to
produce breathing oxygen, drinking water, and rocket fuel from
extraterrestrial matter. Water ice exists in permanently shadowed
craters on the surface of the Moon. On Mars, methane and oxygen can be
created from atmospheric carbon dioxide as long as astronauts bring a
supply of hydrogen. Methane can be used as a rocket fuel or to power
internal combustion engines. It may be possible to construct functional
solar panels from lunar soil. Finally, bricks could be worked from
local materials to provide structural support and protect habitats from
radiation. ISRU will allow easier access to needed resources.

Generating a flow of resources that does not depend on Earth is an
essential step in creating self-sufficient space colonies. In the
initial phase of space settlement, however, many hi-tech assets will
have to be imported from Earth. Nuclear reactors in particular are
extremely complicated machines, especially those intended for space
applications. Nevertheless, space habitats will depend critically on
such technology. When the most complicated of components can be
manufactured outside the Earth’s atmosphere, space habitats will become
truly self-sufficient.

Health Challenges

Living in space presents a number challenges to human health. These are
typically related to radiation, gravity, or sanitation. Although much
experience has been gained over the past decades of spaceflight, some
key uncertainties remain. The fields of astronautical hygiene and space
medicine have emerged to prevent and treat health complications in
space.

Radiation coming from both the Sun and our galaxy can be dangerous to
astronaut health. Many of these particles are deflected away from
humans on the surface by Earth’s magnetic field; the radiation
environment in space, however, is very different. Solar radiation is
especially dangerous only during peak events. To alert astronauts of
these dangerous episodes of space weather, robotic spacecraft could be
used as part of an interplanetary warning system. During such events,
astronauts could retreat to solar “storm shelters.” Galactic cosmic
rays, on the other hand, cannot generally be forecast as well as solar
radiation. Countermeasures to mitigate this threat will have to be more
passive and continuous.

When in orbit, astronauts experience a negligible amount of gravity in
their reference frame. This is not because the local gravitational
field is weak; rather, it is because they are continuously accelerating,
or falling, with gravity. The effect on the body, nevertheless, is the
same as if there were no gravity. The absence of gravity tends to cause
muscle atrophy and a reduction in bone density. For this reason,
astronauts on the ISS exercise for an hour or more per day. Around 45%
of astronauts also report an initial bout of nausea and discomfort upon
reaching space-this is commonly referred to as space sickness. While
serious, the symptoms of space sickness have not been shown to last more
than 72 hours. An effective countermeasure to these effects may be
possible with artificial gravity, which can be generated by spinning a
space habitat. There is no doubt that artificial gravity can be
created, but it has not yet been put into practice; therefore,
unforeseen health challenges may be involved with artificial
gravity.

One of the key weaknesses of the three-person Apollo spacecraft was its
waste management system. Urination was possible through attachable
“relief tubes”, which dumped urine into space. Bags were used to store
fecal matter. Besides being extremely frustrating to use, this system
would not be sanitary for longer periods of time. Waste management is
one area that has significantly improved on space stations since the
Apollo era. Space toilets have been used on the Space Shuttle and ISS.
However, there is still much room for improvement in the design,
redundancy, and placement/integration of space toilets in space
habitats. Likewise, procedures to maintain sanitation in food storage
and trash disposal will need to be continually improved. Finally,
self-sufficient space habitats will require methods of preventing the
spread of contagious illnesses.

Ark I

Ark I is a self-sustaining space habitat being designed to ensure
the survival of humanity in the event Earth becomes uninhabitable. It
is
intended to incorporate several ambitious technologies and techniques to
achieve long-term sustainability. Artificial gravity will be created by
spinning two sets of wheels, which form the living quarters. A complex
ecosystem will be created by bringing plant and animal life into space.
Resources from the Moon and asteroids will be used to reduce the
habitat’s dependence on Earth. Ark I will be powered by nuclear fission
reactors and solar panels. Finally, to guard against the further spread
of any damage, individual modules of the habitat will be capable of
sealing themselves off from the rest of the spacecraft.

Ark I is significant to the establishment of space habitats because it
is one of the first attempts to create a self-sufficient environment and
ecosystem away from the Earth. The project will serve as an impetus to
improve methods of accessing space. It will help to develop new ways of
managing and obtaining resources. It will also serve as a test bed for
advances in astronautical hygiene and space medicine.